Member Project of the Week: Hacking a bargain LED lantern

I’ve often found there’s always a bit of “Tim the Tool Man Taylor” in every hacker.  That is, we all endeavor to make something bigger, badder, and more powerful than anything in it’s class.  Such is the thinking behind this project.  My Mom is an avid shopper, and she is often finding all sorts of bargains.  This time around, she found a camping LED lantern, with 12 LEDs, and a marked luminance of about 30 lumens.

1_first_impression

When I took it out of the box and powered it on, the light was adequate, but not for an LED freak like myself.  Furthermore, I don’t know who designs these things, but they obviously don’t test their own creations.  The lights were mounted facing up, reflecting off a hyperbolic cone.  Unfortunately this means that the majority of the light would be shining out from horizontal upward into the eyes of anyone near it.  As well, none of the light went onto the surface the lantern was sitting on.  These two aspects rendered it quite useless as lanterns go.

2_better_look_at_reflector

Seriously, who designed this and didn’t test it?

My mom was a bit disappointed that she apparently didn’t find as good a bargain as she thought, but I reminded her that with a bit of elbow grease and a few cheap components, I could make it better.  You see, the hardest part of making a good lantern isn’t the light engine, it’s the plastic housing.  The ones she bought already had what I considered to be a pretty nice plastic housing, it just needed an upgrade of the light engine.

Analysis

3_there_is_space

On opening the battery compartment, I noticed that there was some space in it for extra electronics.

4_there_is_hope

Red arrow shows extra space untouched by the 3 D-cell battery carrier.

Knowing that white LEDs run at a forward voltage of 3.4v, and wanting to not use any type of resistive regulation (to avoid wasting power as heat), I knew that A) I’d either be stepping the voltage down to 3.4v or stepping it up to whatever LED cluster I found.  That meant that i needed space in the lantern somewhere for a regulator.  This little nook had enough volume for many switching converter designs, I just needed to find one to fit it.

I immediately went looking on eBay for LEDs to use, and happened upon a lot of 5 of these aluminium core boards that have three 110 lm LEDs on them.  They’re wired in series for a combined brightness of 330 lm. I picked them up for $8.  However, because they’re three 3.4v LEDs wired in series, they’re rated for 10.2v (the post said 9-12v, but 10.2v works the best).  The lantern has a battery carrier that holds 3 D cells.  This gives me an adequate amount of amperage at 4.5v.  Not enough voltage to directly drive the LEDs, so this meant I definitely would need to buy a boost controller.  Again, eBay serves it’s purpose and I was able to nab these LM2577 switchers for about $2.85 each.

5_components

 

Beginning disassembly

5_begin_disassembly

Whenever taking anything apart, make sure you note which screws you pulled from where, and make note of any type of hardware keying like you see here.

6_pay_attention_to_keys

Note the red arrow pointing to the key and slot that the designers put in the top. Make sure you keep track of this for later…

When I cracked this open, I discovered that the hyperbolic cone was not glued to the top (bonus!), but would require cutting if i was going to attempt to put it in the bottom (bogus!).

7_in_elemental_pieces

Elemental pieces. Now it’s time for checking if we can invert the cone.

I centered the hurricane “glass” of the lantern on the cone, then used a fine tip sharpie to draw the outline of the bottom of the glass.

8_testing_fit_drawing_circle

Checking the fit, tracing inner circle with fine tipped sharpie.

9_line_on_reflector

Cut line now marked with fine tip sharpie.

 

I cut relief cuts into the circle before attempting to cut the full circle.  This makes it easier to snap off the chunks as you cut them.  Cutting a circle with a rotary blade on the dremel isn’t easy. To make it easier, I put the dremel in a vise so I could maneuver the reflector around the blade rather than the blade around the reflector. Note my use of the blue nitrile gloves.  When handling any type of chromed plastic reflector, you’ll be sorry if you don’t use gloves.  Once smudged with skin oil it’s hard to impossible get them back into a clean state without scratching them.

10_relief_cuts

Cutting relief cuts before cutting along the sharpie line.

11_test_fit_a

Testing the fit.

12_test_fit_b

Testing the fit with the hurricane in place.

 

13_glue_down_reflector

Gluing down the cone to the bottom reflector with 2 part epoxy.

As with all higher luminance LEDs they emit a fair amount of heat, which is dangerous for the life of the LED.  They do much better if you attach them to a heatsink.  Junk bin to the rescue! CPU heatsinks are useful for many high power LED projects, and they’re usually free if you can find an older computer to scrap.  This heatsink had two “wings” out from the fan, one of which I’ve already removed with a hacksaw to use for this hack.

14_cpu_heatsink

Soldering to the aluminium core board is a hassle, precisely because it’s efficient at wicking away heat.  It means you have to dump a lot of heat into the joint just to get it to marginally flow.  I’m not happy with the quality of these solder joints, but they worked.  Oh, and if it wasn’t obvious, solder FIRST, then attach heat sink otherwise you’d never get solder joints to flow.  😉

I added thermal grease between the heatsink and board, and secured the two together with some dabs of epoxy around the edges and holes in the board.

16_assembled_led_head

I had to remove the switch and battery contact board in order to wire it up to the new driver board.

17_salvage_button_and_contact_board

I soldered it inline with the regulator.  At this stage, I made sure to adjust the output to match the LED forward voltage, in our case, it needed to be adjusted to 10.2v out.  Since these boards are adjustable, you need to attach the voltage you’ll be working with to the input, and adjust the trimmer pot while watching the voltage on a multimeter.

18_add_boost_regulator

If you don’t have this in your hacker’s toolbox, go get some.  Epoxy putty is invaluable, as much for being a filler as it is for being an adhesive.  Be sure to use gloves when kneading it though, as it gets sticky and you don’t want it on your skin.

19_lovely_epoxy_putty

Here you can see the two blobs of the putty that are used to attach the LED assembly to the top.

 20_attach_led_assy_to_top

 

Drill a hole in the back of the reflector to thread the LED head leads through to the battery compartment.

21_make_way_for_leads

Threaded the leads down into the battery compartment as I reassembled the top of the lantern.

 22_thread_leads

 

Here’s where final steps of putting the circuit together take place.

 23_assemble_power_circuit

 

The power board I bought just happened to fit into the switch area without needing to remove any of the plastic.  I always appreciate those little coincidences.

24_final_assembly

The final product, reassembled.

25_reflector_comparison

And finally the two versions side by side.

Two final versions lit up.

26_illuminated

Conclusion:

All told, the entire mod for the first lantern was around 3 hours for a price of about $6 ($1.66 for the LEDs, $2.85 for the boost controller, and about $1.50 in epoxy and epoxy putty). The time spent on subsequent lanterns was about 1 – 1.5 hrs each, now that I know what I’m doing with the design.  Not too shabby.

So did I save any money over buying a higher lumen lantern that was already built?  Yes, and no.  Yes, in pure dollars.  No in terms of time.  But if you don’t understand why someone would spend the time hacking something that might be easier to buy, consider these points.

Hacking something provides:

  • the pleasure of the challenge to make something better.  It gets the creative juices flowing as you attempt to solve problems.
  • the time spent tinkering (far more relaxing than vegging out in front of the TV, IMHO)
  • the feeling of accomplishment when it works and learning from failure when it doesn’t
  • learning how to do things better when you hack on future items
  • it can push you to learn new technologies and techniques in order to get what you want out of the hack
  • the option to actually have a “good enough” approximation when the desired item doesn’t exist, or is prohibitively expensive if it does.
  • prototyping a new idea based on the initial item

And most of all, sometimes you don’t know precisely what you want, until you’ve hacked it!

 

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